ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus GmbHGöttingen, Germany10.5194/acp-7-5003-2007The diurnal evolution of <sup>222</sup>Rn and its progeny in the atmospheric boundary layer during the Wangara experimentVinuesaJ.-F.1BasuS.2GalmariniS.11European Commission &ndash; DG Joint Research Centre, Institute for Environment and Sustainability, 21020 Ispra, Italy2Atmospheric Science Group &ndash; Department of Geosciences and Wind Science and Engineering Research Center, Texas Tech University, USA2809200771850035019This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article is available from http://www.atmos-chem-phys.net/7/5003/2007/acp-7-5003-2007.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/7/5003/2007/acp-7-5003-2007.pdf

The diurnal atmospheric boundary layer evolution of the <sup>222</sup>Rn decaying
family is studied using a state-of-the-art large-eddy simulation model. In
particular, a diurnal cycle observed during the Wangara experiment is
successfully simulated together with the effect of diurnal varying turbulent
characteristics on radioactive compounds initially in a secular equilibrium.
This study allows us to clearly analyze and identify the boundary layer
processes driving the behaviour of <sup>222</sup>Rn and its progeny concentrations.
An activity disequilibrium is observed in the nocturnal boundary layer due to
the proximity of the radon source and the trapping of fresh <sup>222</sup>Rn close
to the surface induced by the weak vertical transport. During the morning
transition, the secular equilibrium is fast restored by the vigorous
turbulent mixing. The evolution of <sup>222</sup>Rn and its progeny concentrations
in the unsteady growing convective boundary layer depends on the strength of
entrainment events.